Communication Technology

Qam Modulator / Demodulator

 

N = 1000;

rnd = 2.1;

mlevel = 4;

 

% signal

x = round((mlevel-1)*rand(1,N));

 

% modulation

bitPerSymbol = sqrt(mlevel);

b = -2.*mod(x,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x./(bitPerSymbol))-bitPerSymbol+1;

xmod = a + i.*b;

 

noise = (rnd*(rand(1,N)-0.5) + rnd*(rand(1,N)-0.5)*i);

 

%adding noise to the modulated signal

xmod_no = xmod + noise;

 

%demodulation

x_qam_ideal = 0:(mlevel-1);

b = -2.*mod(x_qam_ideal,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x_qam_ideal./(bitPerSymbol))-bitPerSymbol+1;

qam_ideal_constellation = a + i.*b;

qam_ideal_constellation = reshape( qam_ideal_constellation, 1, mlevel);

 

n = 0;

z = zeros(size(xmod_no));

 

for k = 1:numel(xmod_no)

    [n z(k)] = min(abs(xmod_no(k) - qam_ideal_constellation));

end

 

z = z-1;

 

xdemod_no = z;

 

err_bit_location = sign(abs(x-xdemod_no));

t = 1:length(x);

 

subplot(2,2,1); plot(real(xmod),imag(xmod),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,2); plot(real(xmod_no),imag(xmod_no),'ro'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,[3 4]);plot(t,x,'bo',t,xdemod_no,'ro');axis([0 length(x) 0 mlevel]);

 



 

N = 1000;

rnd = 0.2;

mlevel = 4;

 

% signal

x = round((mlevel-1)*rand(1,N));

 

% modulation

bitPerSymbol = sqrt(mlevel);

b = -2.*mod(x,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x./(bitPerSymbol))-bitPerSymbol+1;

xmod = a + i.*b;

 

% generating a noise

noise = rnd*randn(1,length(xmod)) + rnd*randn(1,length(xmod))*j;

 

%adding noise to the modulated signal

xmod_no = xmod + noise;

 

%demodulation

x_qam_ideal = 0:(mlevel-1);

b = -2.*mod(x_qam_ideal,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x_qam_ideal./(bitPerSymbol))-bitPerSymbol+1;

qam_ideal_constellation = a + i.*b;

qam_ideal_constellation = reshape( qam_ideal_constellation, 1, mlevel);

 

n = 0;

z = zeros(size(xmod_no));

 

for k = 1:numel(xmod_no)

    [n z(k)] = min(abs(xmod_no(k) - qam_ideal_constellation));

end

 

z = z-1;

 

xdemod_no = z;

 

err_bit_location = sign(abs(x-xdemod_no));

t = 1:length(x);

 

subplot(2,2,1); plot(real(xmod),imag(xmod),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,2); plot(real(xmod_no),imag(xmod_no),'ro'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,[3 4]);plot(t,x,'bo',t,xdemod_no,'ro');axis([0 length(x) 0 mlevel]);

 

N = 1000;

np_dBm = 20.0; % noise power in dBm

mlevel = 4;

 

% signal

x = round((mlevel-1)*rand(1,N));

 

% modulation

bitPerSymbol = sqrt(mlevel);

b = -2.*mod(x,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x./(bitPerSymbol))-bitPerSymbol+1;

xmod = a + i.*b;

 

%generating noise

np = 10 ^((np_dBm - 30)/10);

rnd = sqrt(np/2);

noise = rnd*randn(1,length(xmod)) + rnd*randn(1,length(xmod))*j;

 

%adding noise to the modulated signal

xmod_no = xmod + noise;

 

%demodulation

x_qam_ideal = 0:(mlevel-1);

b = -2.*mod(x_qam_ideal,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x_qam_ideal./(bitPerSymbol))-bitPerSymbol+1;

qam_ideal_constellation = a + i.*b;

qam_ideal_constellation = reshape( qam_ideal_constellation, 1, mlevel);

 

n = 0;

z = zeros(size(xmod_no));

 

for k = 1:numel(xmod_no)

    [n z(k)] = min(abs(xmod_no(k) - qam_ideal_constellation));

end

 

z = z-1;

 

xdemod_no = z;

 

err_bit_location = sign(abs(x-xdemod_no));

t = 1:length(x);

 

subplot(2,2,1); plot(real(xmod),imag(xmod),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,2); plot(real(xmod_no),imag(xmod_no),'ro'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,[3 4]);plot(t,x,'bo',t,xdemod_no,'ro');axis([0 length(x) 0 mlevel]);

 

 

N = 1000;

np_dBm = 20.0; % noise power in dBm

mlevel = 4;

 

% signal

x = round((mlevel-1)*rand(1,N));

 

% modulation

bitPerSymbol = sqrt(mlevel);

b = -2.*mod(x,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x./(bitPerSymbol))-bitPerSymbol+1;

xmod = a + i.*b;

 

%generating noise

np = 10 ^((np_dBm - 30)/10);

rnd = sqrt(np/2);

noise = rnd*randn(1,length(xmod)) + rnd*randn(1,length(xmod))*j;

phase_shift = exp(0.1*pi*j);

 

%adding noise to the modulated signal

xmod_no = (xmod + noise).*phase_shift;

 

%demodulation

x_qam_ideal = 0:(mlevel-1);

b = -2.*mod(x_qam_ideal,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x_qam_ideal./(bitPerSymbol))-bitPerSymbol+1;

qam_ideal_constellation = a + i.*b;

qam_ideal_constellation = reshape( qam_ideal_constellation, 1, mlevel);

 

n = 0;

z = zeros(size(xmod_no));

 

for k = 1:numel(xmod_no)

    [n z(k)] = min(abs(xmod_no(k) - qam_ideal_constellation));

end

 

z = z-1;

 

xdemod_no = z;

 

err_bit_location = sign(abs(x-xdemod_no));

t = 1:length(x);

 

subplot(2,2,1); plot(real(xmod),imag(xmod),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,2); plot(real(xmod_no),imag(xmod_no),'ro'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,[3 4]);plot(t,x,'bo',t,xdemod_no,'ro');axis([0 length(x) 0 mlevel]);

 

N = 1000;

np_dBm = -100.0; % noise power in dBm

mlevel = 4;

 

% signal

x = round((mlevel-1)*rand(1,N));

 

% modulation

bitPerSymbol = sqrt(mlevel);

b = -2.*mod(x,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x./(bitPerSymbol))-bitPerSymbol+1;

xmod = a + i.*b;

 

%generating noise

np = 10 ^((np_dBm - 30)/10);

rnd = sqrt(np/2);

rnd_phase = 0.05;

noise = rnd*randn(1,length(xmod)) + rnd*randn(1,length(xmod))*j;

phase_noise = rnd_phase*randn(1,length(xmod)) + rnd_phase*randn(1,length(xmod))*j;

phase_shift = exp(phase_noise.*pi*j);

 

%adding noise to the modulated signal

xmod_no = (xmod + noise).*phase_shift;

 

%demodulation

x_qam_ideal = 0:(mlevel-1);

b = -2.*mod(x_qam_ideal,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x_qam_ideal./(bitPerSymbol))-bitPerSymbol+1;

qam_ideal_constellation = a + i.*b;

qam_ideal_constellation = reshape( qam_ideal_constellation, 1, mlevel);

 

n = 0;

z = zeros(size(xmod_no));

 

for k = 1:numel(xmod_no)

    [n z(k)] = min(abs(xmod_no(k) - qam_ideal_constellation));

end

 

z = z-1;

 

xdemod_no = z;

 

err_bit_location = sign(abs(x-xdemod_no));

t = 1:length(x);

 

subplot(2,2,1); plot(real(xmod),imag(xmod),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,2); plot(real(xmod_no),imag(xmod_no),'ro'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);

subplot(2,2,[3 4]);plot(t,x,'bo',t,xdemod_no,'ro');axis([0 length(x) 0 mlevel]);

N = 1000;

np_dBm = -100.0; % noise power in dBm

mlevel = 4;

 

% signal

x = round((mlevel-1)*rand(1,N));

 

% modulation

bitPerSymbol = sqrt(mlevel);

b = -2.*mod(x,(bitPerSymbol))+bitPerSymbol-1;

a = 2.*floor(x./(bitPerSymbol))-bitPerSymbol+1;

xmod = a + i.*b;

 

%generating noise

np = 10 ^((np_dBm - 30)/10);

rnd = sqrt(np/2);

rnd_phase = 0.01;

noise = rnd*randn(1,length(xmod)) + rnd*randn(1,length(xmod))*j;

phase_noise = rnd_phase*randn(1,length(xmod)) + rnd_phase*randn(1,length(xmod))*j;

phase_shift = exp(phase_noise.*pi*j);

 

%adding noise to the modulated signal

xmod_no = (xmod + noise).*phase_shift;

 

 

xmod_no_2layer = reshape(xmod_no,2,[]);

cb_01 = 1/sqrt(2).*[1;1];

cb_11 = 1/sqrt(2).*[1;-1];

cb_21 = 1/sqrt(2).*[1;j];

cb_31 = 1/sqrt(2).*[1;-j];

 

cb_02 = 1/sqrt(2).*[1 0;0 1];

cb_12 = 1/2.*[1 1;1 -1];

cb_22 = 1/2.*[1 1;j -j];

 

xmod_no_2layer_cb_02 = cb_02 * xmod_no_2layer;

xmod_no_2layer_cb_02 = reshape(xmod_no_2layer_cb_02,1,[]);

 

figure;

subplot(2,2,1); plot(real(xmod),imag(xmod),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('A');

subplot(2,2,2); plot(real(xmod_no),imag(xmod_no),'ro'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('B');

subplot(2,2,3); plot(real(xmod_no_2layer_cb_02),imag(xmod_no_2layer_cb_02),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('C');

subplot(2,2,4); plot(real(xmod_no),imag(xmod_no),'ro', real(xmod_no_2layer_cb_02),imag(xmod_no_2layer_cb_02),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('D');

 

 

xmod_no_2layer_cb_12 = cb_12 * xmod_no_2layer;

xmod_no_2layer_cb_12 = reshape(xmod_no_2layer_cb_12,1,[]);

 

figure;

subplot(2,2,1); plot(real(xmod),imag(xmod),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('A');

subplot(2,2,2); plot(real(xmod_no),imag(xmod_no),'ro'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('B');

subplot(2,2,3); plot(real(xmod_no_2layer_cb_12),imag(xmod_no_2layer_cb_12),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('C');

subplot(2,2,4); plot(real(xmod_no),imag(xmod_no),'ro', real(xmod_no_2layer_cb_12),imag(xmod_no_2layer_cb_12),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('D');

 

 

xmod_no_2layer_cb_22 = cb_22 * xmod_no_2layer;

xmod_no_2layer_cb_22 = reshape(xmod_no_2layer_cb_22,1,[]);

 

figure;

subplot(2,2,1); plot(real(xmod),imag(xmod),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('A');

subplot(2,2,2); plot(real(xmod_no),imag(xmod_no),'ro'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('B');

subplot(2,2,3); plot(real(xmod_no_2layer_cb_22),imag(xmod_no_2layer_cb_22),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('C');

subplot(2,2,4); plot(real(xmod_no),imag(xmod_no),'ro', real(xmod_no_2layer_cb_22),imag(xmod_no_2layer_cb_22),'bo'); axis([-mlevel/2 mlevel/2 -mlevel/2 mlevel/2]);title('D');